Honestly I am a Souls player, and I really enjoy exploring and finding stuff by myself, however I think it would be great if you "guide" the player indirectly. You could use features like paint or use a certain color like in the Uncharted games. The knives are a good start, or you could use the dialogue system as a hint, for example: "hmm, a key, it may fit in the closed door I saw earlier next to the bed". Something like that could help a lot.
Viewing post in Scale is in the Mind jam comments
The keys all unlock a single thing, and you will know it when your reach the end. The trick is finding all the keys... they really arnt hidden in too sneaky of places, but the trick is only some can be found while big, others while small. You have to time when your shrink or grow against exploration.